Fans of comedy legend Harold Ramis, who died Monday at 69, know him largely from his extensive filmography, which includes classics like Ghostbusters and Groundhog Day. But his presence in Hollywood comedy actually went even further: his presence is found in films like Anchorman and The 40-Year-Old Virgin, even though his name’s not in the credits.

In a 2004 New Yorker profile of Ramis, producer Brian Grazer called him “the father of the modern Hollywood comedy” — because as a key part of the movement to embrace the sensibilities of improvisation, Harold Ramis helped change the look and feel of American humor.

“Other directors may have in the past occasionally used [improvisation], but when it’s really an integral part of how you direct, I think that really affects the sensibility,” says Andrew Alexander, the CEO and executive producer of the Second City, the Chicago-based improv sketch theater that claims Ramis as an alum. “It was giving some power to the actors, to the talent. There may have been a script but he’d get a couple of takes, I’m sure, and then let the actors have some range.”

Before the late 1970s — the era that produced Animal House, Ramis’ first feature script — that riff-heavy style was a rarity. Now, it’s now completely mainstream — and has provided fodder for decades’ worth of blooper reels. Today’s comedy legends, like Groundhog Day star Bill Murray, are often those who can best work with what Alexander describes as the “looseness” of an improv inflection, and the Second City exec cites Judd Apatow and Adam McKay (directors of 40-Year-Old Virgin and Anchorman, respectively) as “devotées” of Ramis and his style.

Nor was his influenced limited to improv, and Andrew Alexander saw that firsthand as a founder of SCTV, Second City’s television sketch show, for which Ramis was head writer. They were both there at the show’s inception in 1976, and Alexander recalls that Ramis’ skill at “layering” was always exceptional. He could combine goofy physical comedy with deep philosophy, and he carried that ability with him to Hollywood, where he helped ensure that some of the most acclaimed comedies of the next decades might be silly — but they would never be dumb.

“The ethos of Second City is to work at the top of your intelligence,” Alexander explains. “Harold had the ability to be smart and at the same time had a good sense of broad [comedy]. It’s an influence almost from the Marx Brothers. He had a certain level of understanding of where physical comedy worked and he had a gift for it as well; it’s the combination of smart and that.”

It’s no wonder that Ramis was able to inspire the next generation of comedians, considering the way his former co-worker describes him. “He was a delight to be around. He was a nurturing mentor-type individual. He got the best out of the talent,” Alexander says. “He was a very encouraging human being.”